The Pakistan-based Lashkar-e-Toiba terrorists have been found to have been complicit in the attacks.

On Sunday, security forces in Jammu and Kashmir region killed two senior separatist militants on the national highway, officials said.

Troops also opened fire after four to five militants tried to cross the border from the Pakistan side.

Every year, rebels call for a boycott of India's Republic Day, which marks adoption of a republican constitution after independence from Britain, and other holidays.

They often carry out attacks on security forces and government buildings.

India will host Kazakhstan President Nursultan Nazarbayev during the celebrations in New Delhi, when India displays its military might. Prime Minister Manmohan Singh, recovering in hospital after a heart bypass operation on Saturday, will not attend the event. Delhi was on high alert.

"This year we have more policemen, more anti-aircraft guns and three helicopters ready to fly out with commandoes in case of any emergency," Rajan Bhagat, the Delhi Police spokesman, said.

Security was tight in Mumbai. Police patrolled outside high-profile public places. The main railway station, a Jewish centre and two five star hotels were targets of the militants in the November attacks.

"We have called in for additional forces and we will be keeping an eye out," said KL Prasad, Mumbai police commissioner.

The Indian coastguard and navy stepped up patrols. The Mumbai attackers had entered India by sea.

Troops and police stepped up patrols across the north-east Indian region's eight states, guarding bridges, railway stations and airports.

In Kashmir, separatist violence has declined since India and Pakistan, who claim the region in full but rule it in parts, launched a peace process in 2004. But people are still killed almost daily in fighting between militants and soldiers.